1. Field of the Invention
The inventions disclosed herein relate to apparatus and methods for forming thermoplastic liners and thermoplastic liners formed thereby, more particularly, apparatus and methods for forming micro spike thermoplastic liners and micro spike thermoplastic liners formed thereby.
2. Description of the Prior Art
Thermoplastic liners have been used extensively in the prior art to seal tunnels, excavation sites, landfills, and the like. Typically, to cover the desired area with the thermoplastic liner, continuous lengths of the liner are placed in either partial overlapping or abutting contact and caused to be connected in some leak-proof method, such as welding. It can be readily appreciated that some concerns arise with the use of thermoplastic liners. First, since thermoplastic liners must be used at various grades, the liners must be provided with at least one surface which can frictionally engage the graded surface and maintain the liner in a desired location. Second, due to the tremendous area often required to be covered by a thermoplastic liner, the costs of manufacturing such liners needs to be minimized.
Several approaches have been taken in the prior art to produce an acceptable thermoplastic liner. For example, a repeated embossed pattern is provided on one surface of the thermoplastic liner, such as shown in U.S. Pat. No. 4,612,152 to Kawabata, et al. Prior art embossing techniques, however, suffer from several drawbacks. First, the underlying base substrate of the thermoplastic liner must be substantially deformed to achieve a desired embossed pattern, which may result in damage to the base substrate. Second, typically, the repetition of an embossed pattern creates regular, continuous grooves in the thermoplastic liner between the embossed projections. Over time, the continuous grooves may cause the underlying engaged material, such as soil, to furrow therein, with further furrowing allowing movement of the liner relative to the underlying material and eroding the gripping force thereof. Third, although the process of embossing thermoplastic seeks to define sharp edges in the embossed substrate, the edges are often formed rounded with a small radius. This effect, of course, reduces the grip of the film on underlying material.
To overcome the shortcomings of the prior art, it is an object of this invention to provide a roughened thermoplastic liner formed with a plurality of even-spaced projections, which are each irregularly formed.
It is also an object of the subject invention to provide a calendering roll for forming a roughened thermoplastic liner having a plurality of evenly-spaced projections, which are each irregularly formed.
It is yet another object of the subject invention to provide a method for forming a thermoplastic liner having a roughened surface with a plurality of evenly-spaced projections, with each projection being irregularly formed.
It is still a further object of the subject invention to provide a method for forming a calendering roll which is for forming a thermoplastic liner having a roughened surface with a plurality of evenly-spaced projections, with each projection being irregularly formed.